Influenza virus is a RNA virus belonging to Family Orthomyxoviridae which causes inflammation in respiratory system. This is a highly infectious virus that infects others via direct communication through air from cough or saliva of the infected ones or via indirect communication through anything that is touched by the infected ones. The incubation period of this virus is 24˜30 hours and serotype of the virus is divided as type A, type B, and type C. Type B and type C are confirmed to infect only human, while type A can infect not only human but also various species of mammals including horse, pig, and others, and also various species of domestic poultry and wild birds (Selmons et al., Avian Dis., 18(1), p. 119-124, 1974; Webster R G et al., Microbiol Rev., 56(1), p. 152-179, 1992).
The classification of serotype of type A influenza virus depends on the two kinds of proteins observed on the surface of the virus, which are Hemagglutinin (HA) and Neuraminidase (NA). Type A virus can be divided into 144 different serotypes (16 kinds of HA and 9 kinds of NA). HA aids the virus to be attached on somatic cells, while NA helps the virus to invade into the cells (Alexander D J, Vet. Microbiol., 74(1-2), p. 3-13, 2000). The natural normal host for type A influenza virus is wild water birds such as duck and seagull. From the epidemiological studies of influenza virus infection in wild birds over the world, it was confirmed that all the existing 16 kinds of HA and 9 kinds of NA were found in wild birds (Selmons et al., Avian Dis., 18(1), p. 119-124, 1974). Avian influenza virus classified as type A is the zoonosis virus which is divided into three major groups (Alexander D J, Vet. Microbiol., 74(1-2), p. 3-13, 2000); which are non-pathogenic avian influenza that causes light respiratory symptoms when it infects chickens, low pathogenic avian influenza (LPAI) that causes 1˜30% mortality and egg drop syndrome, and highly pathogenic avian influenza (HPAI) called “Bird Flu” that shows high lethality of at least 95%. Particularly, HPAI is classified as List A disease by OIE (Office International des Epizooties) and as 1st class contagious animal disease in Korea.
Since 1980s, HPAI has been reported world-widely including USA (1983), Australia (1985, 1992, 1994 and 1997), Mexico (1994), Pakistan (1994 and 2004), Hong Kong (1997 and 2001), Italia (1997 and 1999), Netherland (2003), Belgium (2003), Germany (2003), and Canada (2004). In addition, starting with Korea (December, 2003), almost all the East-South Asian and Far East Asian countries including Vietnam, Japan, Thailand, Cambodia, Laos, Indonesia, and China reported the break-out of serotype A/H5N1 HPAI all at the same time in 2004. In particular, HPAI broken out in Vietnam and Thailand, unlike typical HPAI broken out in Korea and Japan at that time that has been characterized as not being infectious to human, was confirmed as a mutant avian influenza (mutant A/H5N1 HPAI) that was infectious to human via contact with infected birds. As of March, 2004 in Vietnam, 15 out of 22 people infected with the mutant form by the contact with the infected birds were dead and 8 out of 11 people were also killed in Thailand as well, worrying all the countries. The frequency of HPAI outbreak is 10 times higher than before. Since 2001, HPAI outbreak has been reported every year world-widely. Therefore, it is required to develop a novel prevention method which is effective in controlling HPAI (Song C S et al., Korean J. Poult. Sci., 31(2), p. 129-136, 2004).
Some serotypes of influenza virus, which causes problems in birds, cause even death in human after developing flu symptoms. Some mutant forms originated from three serotypes of avian influenza virus such as A/H7N7, A/H9N2, and A/H5N1 so called “Hong Kong avian influenza” are assumed to be infectious to human. Therefore, studies on such mutant virus forms originated from the above three serotypes have been eagerly going on word-widely (Suarez D L et al., J. Virol., 72(8), p. 6678-6688, 1998).
In the meantime, novel influenza that has been now prevailing all over the world since it was first found in Mexico in spring of 2009 is influenza type A subtype H1N1 having type 1 hemagglutinin (H1) and type 1 neuraminidase (N1) (Hereinafter, the said novel influenza A virus is called ‘2009 NIH1 influenza virus’). The 2009 NIH1 influenza virus is a kind of virus in which genetic materials of influenza viruses originated from human, swine, and birds are mixed. At this time swine is called as “mixing vessel”. Thus, it was first named as swine influenza. However, since there was no proof saying that this virus is directly delivered to human from infected swine or delivered to swine from infected human or related to swine whatsoever, WHO used to call it novel influenza A (H1N1). From the sequence analysis of 2009 N1H1 influenza virus, it was confirmed that HA gene includes a certain sequence that is infectious to human, suggesting the possibility of infecting human. HA gene does not contain dibasic amino acid, the typical amino acid of highly pathogenic virus, but comprises drug resistant gene against amantadine and rimantadine. The virus was also confirmed not to have any mutation in NS1 and PB2 genes in relation to pathogenicity, suggesting that the virus was not highly pathogenic. 2009 NIH1 influenza virus is infectious through respiratory system and is highly contagious compared with the conventional influenza A virus. The symptoms of this virus are similar to those of the conventional influenza virus, for example high fever, cough, etc. To prevent the infection, personal hygiene including hand-washing and wearing a mask is required. It is recommended to treat the virus infection to use antiviral agents such as Tamiflu and Relenza.
Once infected with influenza virus, each organ in respiratory system loses its resistance, resulting in the development of complications such as bronchitis, laryngopharyngitis, and pneumonia. Particularly, chronic disease patients, aged people, children, and long-term hospitalized patients are in high risk since their immunities are very weak. Therefore, studies to prevent influenza are going on in the aspects of biosecutity and influenza vaccine. However, to get vaccine shot, proper timing is important as well as the prediction of the kind of prevailing influenza virus, which are troublesome.
Efforts have been made world-widely to develop an antiviral agent. Up to date, lamibudine used for the treatment of HIV-1 and hepatitis B, gancyclovir used for the treatment of herpes virus infection, and ribavirin used for the treatment of respiratory syncytial virus infection and also used for the urgent care of diverse virus infections have been approved and now are on the market. In addition, amantadine approved for the treatment of influenza virus A and its analogue rimantadine, zanamivir (Relenza) artificially synthesized as an influenza virus neuraminidase inhibitor, and oseltamivir (TAMIFLU™) are also on the market. Amantadine and rimantadine are designed to inhibit the functions of M2 ion channel protein of influenza virus, which are representative antiviral agents suppressing in vivo proliferation of influenza virus. These two antiviral agents are only effective for serotype A influenza virus and not effective at all for serotype B influenza virus that does not contain M2 protein. There is another problem in using amantadine and rimantadine. That is, with the use of those drugs, a mutant virus is easily generated whose M2 ion channel protein is not affected by those drugs. Zanamivir and oseltamivir, developed to overcome the above problem, are designed to inhibit the functions of neuraminidase, which became representative antiviral agents inhibiting the proliferation of influenza virus in vivo. These two antiviral agents are known to be effective in inhibiting all of 16 kinds of serotype A influenza virus and all of serotype B influenza virus. However, zanamivir needs to be inhaled or injected intravenously, which is not an easy pathway. In the meantime, oseltamivir can be orally administered, but according to the recent reports, side effects such as vomiting and dizziness are accompanied with the oral administration and resistant virus has been also generated (Ward P et al., J. Antimicrob. Chemother., 55(suppl), p. i5-i21, 2005). Therefore, it is important to develop a safe natural agent along with the vaccine and therapeutic agents to increase human immunity and to reduce death rate upon pandemic of such virus.
To treat influenza in Oriental Medicine, different kinds of medicinal herbs are boiled together and the extract therefrom is used, which is exemplified by Insampaedoksan, Gumiganghwalsan, Galgeun-tang, Mahwang-tang, Daecheongryong-tang, Seungmagalgeun-tang, Chungjogupae-tang, Yihyangsan, and Baekhogainsam-tang. Many kinds of medicinal herbs are used, and these are more to increase immunity of human body than to act as an antiviral agent. Thus, it is urgent request to develop a novel drug to prevent and/or treat influenza virus-induced disease more fundamentally.
Thus, the present inventors investigated the effect of medicinal herbs used in Oriental Medicine on the activity of influenza virus. As a result, the present inventors confirmed that the herbal extract containing Epimedium koreanum had excellent preventive and/or therapeutic effect on diseases caused by various types of influenza viruses, leading to the completion of this invention.